1. Field of the Invention
The present invention relates to a control apparatus for an automatic transmission, which controls the oil pressure for operating the clutch for changing the speed of the automatic transmission of a vehicle, and to a control method.
2. Prior Art
According to a conventional control method of this type as taught in, for example, Japanese Patent Laid-Open No. 25662/1992, the operation oil pressure to be supplied to a friction coupling device has been controlled by learning, so that a deviation decreases between a target value of change in the torque and a practical value at the start of the feedback control operation.
According to the control method taught in Japanese Patent Laid-Open No. 25662/1992, however, the deviation increases due to a change in the opening degree of the throttle and a change in the oil temperature in the automatic transmission, leaving a problem in that the control stability is impaired in the feedback control operation when the speed is being changed.
An object of the present invention is to provide an apparatus for controlling a transmission which suppresses a shock in the change of speed by bringing a target value of change in the torque into agreement with a practical value at the start of the feedback control operation, and a method thereof.
There occurs a hunting or a change in the torque when a deviation is great between a target value and a practical value at the time of starting the feedback control operation. In the conventional feedback operation for controlling the transmission, the oil pressure fed to a friction coupling device is brought into match, so that the deviation decreases between the two. However, the practical oil pressure fluctuates with respect to the instructed oil pressure due to accuracy of the actuator. Namely, the feedback control operation loses stability due to a fluctuation in the oil pressure. It has, therefore, been urged to provide an actuator having improved accuracy. According to the present invention, however, there does not occur a deviation between the two since a practical torque value is used as an initial target value. This permits the operation oil pressure to be roughly set to some extent, making it possible to use an actuator that is constructed at a lower cost.
According to the present invention, the above-mentioned problem is solved by an apparatus that is described below. That is, the present invention provides an apparatus for controlling the oil pressure of an automatic transmission, having a pressure-regulating instruction generating means which changes the speed by coupling or decoupling a predetermined friction coupling device in the automatic transmission coupled to an engine, regulates the oil pressure that acts on said friction coupling device at the time of changing the speed, and changes the pressure-regulating characteristics, and means for so controlling the output shaft torque of said automatic transmission as to follow a target value, said apparatus for controlling the oil pressure of the automatic transmission further comprising:
a speed-changing detecting means for detecting that said automatic transmission is changing the speed;
a torque operation means for operating the output shaft torque of said automatic transmission;
a point-of-inflection recognizing means for recognizing a point of inflection of the output shaft torque during the change of the speed;
a target value-setting means for setting a target value of the output shaft torque of said automatic transmission; and
an initial value-setting means for setting said initial target value at a moment of said point of inflection.